U.S. Pat. No. 4,921,962 claims a process for the formation of N-hydrocarbyloxy derivatives of sterically hindered amines in which a hindered amine or N-oxyl substituted hindered amine is reacted with a hydrocarbon solvent in the presence of a hydroperoxide and a metal carbonyl, metal oxide or metal alkoxide catalyst.
U.S. Pat. No. 5,374,729 describes a process for the preparation of N-methoxy derivatives of sterically hindered amines from the reaction of hindered amine N-oxyl compounds with methyl radicals produced by the combination of aqueous hydrogen peroxide and a peroxide-decomposing transition metal salt in the presence of dimethyl sulfoxide.
D. H. R. Barton, et al., in Tetrahedron, 1996, 52, 10301-12, describe the formation of N-alkoxy substituted sterically hindered amine derivatives obtained by the reaction of unactivated hydrocarbons with iron(II) and iron(III) salts or metal-ligand complexes, hydrogen peroxide, and pyridine/acetic acid or pyridine/picolinic acid in the presence of 1-oxyl-2,2,6,6-tetramethylpiperidine (TEMPO).
U.S. Pat. No. 6,166,212 claims a process in which an N-oxyl compound is reacted with a peroxide or organic hydroperoxide and a catalytic amount of a metal salt or metal-ligand complex in an alcohol solvent to synthesize N-hydroxyalkoxy substituted hindered amine stabilizer molecules.
U.S. Pat. No. 6,211,378 teaches an environmentally friendly process for the preparation of 4-functionalized sterically hindered N-hydrocarbyloxyamine derivatives of 2,2,6,6-tetramethylpiperidines using hydrogen peroxide to oxidize a hindered amine to an N-oxyl compound which is reacted with one equivalent of a compound having an allylic, benzylic, or activated methine hydrogen.
U.S. Pat. Nos. 5,629,426, 5,654,434, and 5,777,126 disclose a process for the formation of N-oxyl sterically hindered amines from hindered amines using aqueous hydrogen peroxide.
N-hydrocarbyloxy derivatives of 2,2,6,6-tetramethylpiperidines can be made in a variety of ways, which include the following: a) catalytic hydrogenation of an N-oxyl hindered amine to form a hydroxylamine, as taught in U.S. Pat. No. 4,831,134, followed by alkylation of the hydroxylamine using a strong base such as sodium hydride and an alkyl halide, as taught in U.S. Pat. No. 5,204,473; b) reaction of 2 equivalents of N-oxyl hindered amine with tributyltin hydride and an iodo- or bromo-substituted hydrocarbon in an inert solvent such as chlorobenzene, as taught in U.S. Pat. No. 5,021,577; c) heating a solution of an organic peroxide, such as di-tert-butyl peroxide, an N-oxyl compound, and a hydrocarbon with abstractable hydrogen atoms as disclosed in U.S. Pat. No. 5,204,473; d) heating a mixture of an N-oxyl hindered amine, an organic hydroperoxide, a catalytic amount of a molybdenum catalyst, and a hydrocarbon solvent with abstractable hydrogen atoms as taught in U.S. Pat. No. 4,921,962; and e) reaction of a mixture of iron(II) perchlorate or iron(III) chloride, hydrogen peroxide, acetic acid or picolinic acid, adamantane or cyclohexane and an excess of pyridine solvent in the presence of N-oxyl-2,2,6,6-tetramethylpiperidine (TEMPO), as disclosed by Barton, et al., in Tetrahedron, 1996, 52, 10301-12.
The instant process involves the formation of N-hydrocarbyloxy hindered amine derivatives by reacting a mixture of an N-oxyl hindered amine with hydrogen peroxide and a catalytic amount of metal salt, oxide, or metal ligand complex, and where needed, a mineral acid or organic acid, in the presence of a hydrocarbon and a cosolvent.
The instant process does not require specialized reagents such as alkyl halides, sodium hydride, or tributyltin hydride. The instant process offers the advantage of using hydrogen peroxide instead of a more expensive tertiary alkyl hydroperoxide. Furthermore, the by-product from hydrogen peroxide is water, whereas tertiary alkyl hydroperoxides produce alcohol by-products, such as t-butyl alcohol from t-butyl hydroperoxide. These alcohols must be separated from the desired reaction product and disposed of. Products made from solvents which boil near or below 100° C., such as cyclohexane and heptane, are most efficiently made by carrying out the reactions in a pressure vessel in order to obtain the desired 100-150 degree reaction temperature. The instant process does not require a pressure vessel for lower boiling hydrocarbon solvents. For example, reactions with cyclohexane can be effectively carried out at 60° C. The use of lower reaction temperatures in the instant process requires less energy and eliminates safety issues specifically associated with the use of pressure vessels.
The instant process does not require the use of substantial amounts of toxic solvents, like pyridine. In addition to its toxicity, pyridine is difficult to remove from the reaction mixture because of its relatively high boiling point, 115° Celsius. Barton, et al., remove pyridine by an acid work-up involving concentrated sulfuric acid and ice. The instant process obtains excellent yields of N-hydrocarbyloxy products with methanol (bp 65°) or acetonitrile (bp 81°) as a cosolvent. These materials are easy to remove by a solvent strip or simple distillation and have the advantage of being water-soluble.
The instant process does not require the addition of additives such as ascorbic acid or zinc.
The instant invention, though primarily concerned with the formation of N-hydrocarbyloxy amines from their N-oxyl precursors, also teaches a two-step process in which a hindered amine is oxidized to the intermediate N-oxyl compound. The N-oxyl compound is not isolated prior to conversion to the N-hydrocarbyloxyamine. Hydrogen peroxide is an inexpensive and efficient reagent for such an oxidation.
U.S. Pat. Nos. 5,629,426, 5,654,434, and 5,777,126 disclose a process for the formation of N-oxyl sterically hindered amines from hindered amines using aqueous hydrogen peroxide, a metal passivator, an ammonium or alkali carbonate or bicarbonate, and water as the solvent.
Published methodologies for the oxidation of hindered amines to N-oxyl compounds using hydrogen peroxide and sodium tungstate are described by Yoshioka, et al., in Bull. Chem. Soc. Japan, 1972, 45, 636-638 and Rauckman, et al., in Synthetic Communications, 1975, 5, 409-413.
U.S. Pat. No. 4,961,962 teaches the conversion of hindered amines to N-hydrocarbyloxy derivatives, without isolation of the intermediate N-oxyl compound, using organic hydroperoxides.
The instant invention provides an improved process for the preparation of sterically hindered N-hydrocarbyloxyamines.